In the last four months, Christchurch has received more than two thirds of the city's average annual rainfall, according to updated MetService data.

A faulty rain gauge at Christchurch Airport has been under-reporting the amount of rainfall in the city.

Meteorologist John Law said a technical team had switched over to a backup version, which had been recording ''much more reasonable'' figures.

Rainfall records from the backup gauge showed 15mm of rain fell in January, 56.8mm in February, 151.2mm in March and 216.6mm in April. Adding a couple of days from May into the mix brought the total up to 442.4mm.

MetService meteorologist Daniel Corbett said that was more than double the normal amount of rainfall at the airport for this time of year - about 200mm.

Corbett said Christchurch Airport "typically" received about 620 millimetres of rain a year, so at more than 440mm already, "we're running well ahead of what would be normal".

"It has certainly been a very, very wet couple of months. There's no doubt about that," he said.

''We have had weather system after weather system and the ones that have brought the rain have really brought it."

A significant amount, 72.8mm - almost three inches - fell on April 28.

Further south, Winchmore inland from Ashburton, had its wettest April on record. Figures from the National Institute of Water and Atmospheric Research (Niwa) show a rainfall of 301mm, six times normal.

The Niwa figures also show that Christchurch had its second wettest April since records started in 1863, recording five times the normal amount with 224mm.

The South Island was also warmer than usual. Overnight temperatures were well above normal in many places, with a number of weather stations reporting mean minimums 2-3C above the normal for April.

"A likely contributing factor to the warm overnight periods is the abundant moisture in the form of cloud and rain as well as the influence of an ex-tropical cyclone," the Niwa summary said.

BY THE NUMBERS

Total rainfall for month (average for month)

January 15mm (46mm)

February 56.8mm (43mm)

March 151.2mm (55mm)

April 216.6mm (54mm)

* The MetService provided an incorrect rainfall figure in a previous story published on press.co.nz. It said the airport, on average, received about 443mm of rain a year. The correct figure is 620mm.